1. Field of the Invention
The present invention relates to a reflection characteristic measuring apparatus for measuring a characteristic of a sample surface such as a gloss of the sample surface.
2. Description of the Related Art
There is known a reflection characteristic measuring apparatus for measuring the gloss of a sample surface. FIG. 18 is a diagram showing a construction of a conventional reflection characteristic measuring apparatus 100.
As shown in FIG. 18, the reflection characteristic measuring apparatus 100 includes an incident-side optical system 101 and a reflection-side optical system 102. The incident-side optical system 101 outputs light toward a sample surface S set in a proper position, with a certain angle with respect to the normal G passing a certain point on the sample surface S. The reflected light from the sample surface S is incident onto the reflection-side optical system 102 disposed at a position with a certain angle with respect to the normal G.
The incident-side optical system 101 and the reflection-side optical system 102 have diaphragms 103 and 104, respectively. The diaphragm 103 of the incident-side optical system 101 is adapted to direct the light from a light source 105 toward the sample surface S within a predetermined opening angle. The diaphragm 104 of the reflection-side optical system 102 is adapted to direct the reflected light from the sample surface S toward a light receiving surface of a light detector 106 within a predetermined light detection angle. The gloss of the sample surface S is measured, using an output from the light detector 106 which has received the thus-regulated reflected light.
Japanese Unexamined Patent Publication No. Hei 8-29258 discloses an apparatus for measuring the color and the gloss of a sample surface to be measured. The apparatus is provided with a line sensor for receiving light reflected from the sample surface in the direction of the normal, and first and second illumination optical systems disposed at such positions as to illuminate the sample surface with light inclined by 45 degrees with respect to the normal. The one of the illumination optical systems includes a mirror for switching over an optical path between a first position in which the light from a light source provided in the illumination optical system is guided to the sample surface, and a second position in which the light incident to the illumination optical system is reflected to a position different from the position of the light source; and an image sensor for receiving the light reflected from the mirror in the second position. In measuring the color of the sample surface, the first and the second illumination optical systems irradiate the light, with the mirror being set in the first position, and the line sensor receives the light reflected from the sample surface. In measuring the gloss of the sample surface, the first illumination optical system irradiates the light, with the mirror being set in the second position, and the image sensor receives the light reflected from the sample surface.
In use of the reflection characteristic measuring apparatus shown in FIG. 18, as shown in FIG. 19, if the setting position of the sample surface S is tilted by the angle θ, the direction along which the reflected light from the sample surface S is incident onto the reflection-side optical system is tilted by the angle 2θ with respect to the original condition before the tilting. In FIG. 19, the diaphragm 104, the light detector 106, and the like are not illustrated. In this condition, as shown in FIG. 20, assuming that the focal length of a lens element 107 of the reflection-side optical system 102 through which the reflected light is directed toward the light detector 106 is defined as f, the focus position is displaced by f×tan 2θ on the focus plane with respect to the focus position M of reflected light obtained in a condition that the sample surface S is not tilted. In FIG. 20, the solid line shown by the symbol A1 indicates reflected light to be obtained in the case where the sample surface S is not tilted, and the dotted line shown by the symbol A2 indicates reflected light to be obtained in the case where the sample surface S is tilted by the angle θ.
In the conventional measuring apparatus 100, the dimensions of the aperture of the diaphragm 104 provided in the reflection-side optical system 102 are fixed. Accordingly, if the sample surface S is tilted as mentioned above, the amount of reflected light detected by the light detector 106 is varied with respect to a proper condition that the sample surface S is not tilted relative to the measuring apparatus 100. This results in failure of accurate detection of the gloss of the sample surface S.
Also, even if the sum of the amount of reflected light detected by the light detector 106 is identical concerning sample surfaces whose gloss is to be measured, the sample surfaces include sample surfaces having a relatively small ratio of specular reflection light component to diffusion light component as shown in FIG. 21A, and sample surfaces having a relatively large ratio of specular reflection light component to diffusion light component as shown in FIG. 21B. The curves (1) and (2) in FIGS. 21A and 21B show magnitudes of intensities of reflected light with respect to a distance from the reflection point Z. As is obvious from FIGS. 21A and 21B, the intensity of reflected light passing a relevant point on the curve (1), (2) is increased, as the distance from the reflection point Z to the point on the curve (1), (2) is increased.
In the conventional reflection characteristic measuring apparatus 100, the dimensions of the aperture of the diaphragm 104 provided in the reflection-side optical system 102 are fixed, and the gloss of the sample surface is measured based on the sum of light passing through the aperture. Accordingly, if the sum of the amount of reflected light detected by the light detector 106 is identical concerning the sample surfaces to be measured, all the sample surfaces are determined to have the same degree of gloss, which makes it impossible to distinguish the sample surfaces one from the other. Even with use of the apparatus disclosed in the above publication, the drawback cannot be overcome.